The present invention relates generally to aqueous metal cleaning compositions. In particular, this invention is directed to aqueous metal cleaning compositions useful in so-called parts washers and, in particular, to parts cleaners, which are particularly adapted to be used by professional or semi-professional mechanics, as well as homeowners, farmers, ranchers, hobbyists, or other such users.
Parts washers of various kinds are known to those skilled in the art as having great utility for mechanics and others working in a variety of occupations, particularly those working in industrial plants, maintenance and repair services, and the like. At one time, the development of parts washers was based on an attempt to insure reasonable convenience in use and good cleaning action. Many garages, service stations and the like owned and used soak tanks, so-called hot tanks, or immersion type parts cleaners, usually of more or less elaborate configuration.
U.S. Pat. No. 3,522,814 to Olson and assigned to Safety-Kleen Corp. described a new concept in parts washers insofar as it related to a parts washer construction which included among other novel features, a construction particularly adapted to facilitate extremely rapid and simple machine service. An entire industry was then founded on the concept of a parts washer which was designed so that it could be economically and effectively serviced by route men with little, if any, specialized training. It was discovered that there was an enormous market among garage and service station owners, automobile dealers, and industrial plant operators for a parts washer which could be serviced safely and without disrupting operations, either by way of downtime or physically interfering with such operations.
The ideal parts washer is reliable, safe, quiet and effective in use, is free from environmental objections, and perhaps most importantly, can be serviced readily as just discussed. While the parts washer described in U.S. Pat. No. 3,522,814 has achieved phenomenal success in commercial markets, various improvements have been made and are disclosed in several U.S. patent including; U.S. Pat. No. 4,096,873; U.S. Pat. No. 4,160,603; U.S. Pat. No. 4,261,378; U.S. Pat. No. 4,462,415 and U.S. Pat No. 4,637,413.
The device described in the foregoing patent to Olson has been extremely successful in the industry by providing a parts washer having economic and hazard-free operation to subject parts to be cleaned to a circulating flow of solvent and the like. In operation of the device described in the Olson patent, a pump circulates a solvent from a drum into a sink containing parts for cleaning. A flow of solvent is directed against the parts and drains from the sink through a filtering medium for return to the drum. In the event of a fire, the washer described in U.S. Pat. No. 3,522,814 is capable of automatically closing a cover over the sink to minimize its effect.
Although the washer of U.S. Pat. No. 3,522,814 provides highly improved operative characteristics during cleaning, it has been found that it becomes advantageous to subject parts for a period of time to a soaking bath in a solvent or other fluid under certain encountered conditions such as, for example, where an extraordinary amount of foreign material is affixed to the elements to be washed. In known techniques, such soaking is accomplished generally by positioning the parts in a volume of fluid in an opened container from which undesired solvent fumes may be evaporated to the surroundings with a resulting costly depletion of fluid and the danger of uncontrolled fire or spilling being present. The prevention of such uncontrolled soaking in an open vessel has become more advantageous in the light of numerous government regulations governing the use of substances in the form of solvents such as required by O.S.H.A. and the like. Thus, U.S. Pat. No. 4,261,378 mentioned above, provides a highly advantageous accessory which allows effective washing of parts with drainage such as disclosed in U.S. Pat. No. 3,522,814, with the alternative mode of operation as a highly effective and non-hazardous soaking device.
The accessory disclosed in U.S. Pat. No. 4,261,378 overcomes the foregoing problems by permitting a conventional washer to operate in its normal circulating mode without a substantial soaking action, with the added improvement of selectively retaining a quantity of solvent in a sink for a soaking application. The soaking operation provided by the accessory is accomplished by a device which prevents the escape of fumes to the surroundings and the costly evaporation of the cleaning solvent, and which at the same time minimizes the danger of fire and other accidents. In addition, the accessory provides improved soaking by maintaining a predetermined level of fluid over the parts to be cleaned with constant circulation of the solvent. U.S. Pat. No. 4,261,378 is herein incorporated by reference.
Existing solvents, with or without special additives, are adequate to achieve good cleaning of most dirty, greasy, mechanical parts. A great number of these solvents are employed to produce metallic surfaces free from contamination. These wash solvent compositions generally employ various halogenated hydrocarbons and non-halogenated hydrocarbons, of significant quantity industry wide for cleaning and degreasing of the metal surfaces, and the degree of success with each of these wash solvent compositions is generally dependent upon the degree of cleanliness required of the resultant surface.
Recently, however, the various hydrocarbon and halogenated hydrocarbon metal cleaning compositions previously employed have come under scrutiny in view of the materials employed, and in particular, the environmental impact from the usage of the various materials. This is particularly so in the case of parts cleaning which is done in closed environments such as garages and the like or for even home usage in view of the close human contact. Even the addition of devices to parts washers which can reduce spillage, fire and excessive volatilization of the cleaning solvent are not sufficient to alleviate present environmental concerns.
Although the halogenated hydrocarbon solvents such as chlorofluorocarbons (CFCs) and trichloromethane, methylene chloride and trichloroethane (methyl chloroform) are widely used in industry for metal cleaning, their safety, environmental and cost factors coupled with waste disposal problems are negative aspects in their usage. A world-wide and U.S. ban on most halogenated hydrocarbon solvents is soon in the offing by virtue of the Montreal Protocol, Clean Air Act and Executive and Departmental directives.
The non-halogenated hydrocarbon solvents such as toluene and Stoddard solvent and like organic compounds such as ketones and alcohols on the other hand are generally flammable, have high volatility and dubious ability to be recycled for continuous use. These, plus unfavorable safety, environmental and cost factors, put this group of solvents in a category which is unattractive for practical consideration. Most useful organic solvents are classified as volatile organic compounds (VOCs) which pollute the atmosphere, promote formation of toxic ozone at ground level, and add to the inventory of greenhouse gases.
In order to eliminate the various negative aspects of the known chemical washing and degreasing systems, it has, therefore, been suggested that an aqueous detergent system be used so as to overcome some of the inherent negative environmental and health aspects of prior art solvent cleaning systems. Unfortunately, aqueous cleaning systems are not without their own problems as related to used thereof in metal cleaning systems including use in the parts washers described above. For example, certain of the aqueous cleaners are exceedingly alkaline having pHs of 13 and above such as sodium hydroxide or include organic solvents such as alkanolamine, ethers, alcohols or glycols and the like. Besides being highly corrosive, the exceedingly high alkaline aqueous solutions are highly toxic and can be dangerous to handle requiring extreme safety measures to avoid contact with skin. Organic solvent-containing aqueous cleaners present the problems regarding toxicity or the environment as expressed previously. On the other hand, it is most difficult to obtain an aqueous detersive solution at moderate pH which is effective in removing the greases and oils which contaminate metal including metal engine parts and which would not be corrosive to the metal substrate.
U.S. Pat. No. 5,230,824 discloses an aqueous metal cleaning composition for removing oil, dirt and grinding debris from razor blades and which comprises an alkalinity providing agent, a chelating agent, a hydrotrope and a defoaming agent together with a non-ionic surfactant. The preferred alkalinity providing agents include the alkali metal hydroxides, the alkali metal silicates and the alkali metal carbonates. The non-ionic surfactant comprises the ethoxylates of C.sub.9 -C.sub.16 tertiary thiols as described in U.S. Pat. Nos. 4,575,569 and 4,931,205.
While the ethoxylated thiol surfactants have been found to be highly effective in aqueous solution for the removal of grease from substrates, particularly metal surfaces, one drawback of these surfactants is the very unpleasant odor which the surfactant imparts to the product such as an aqueous concentrate to which the surfactants are added as well as to the more dilute wash solutions which contain these ethoxylated thiol surfactants. The unpleasant odor significantly reduces the types of product to which the ethoxylated thiols can be added. This would be particularly so of the parts washing systems such as described above and developed by Safety-Kleen Corp. which have been very successful in the commercial service area including garage and service stations, automobile dealers and the like. In the typical enclosed environments which such commercial enterprises operate, the unpleasant odor of the ethoxylated thiol surfactants would not be tolerated and the use thereof would greatly hinder the commercial operation. On the other hand, the excellent grease removing ability of these surfactants render them most useful in aqueous cleaning systems for parts washing devices and methods of metal cleaning.
Accordingly, it is an object of the present invention to provide an aqueous metal cleaning composition which is effective to clean grease, oil and other contaminants from a metal surface without being excessively corrosive to the substrate and irritating to human skin.
Another object of the invention is to provide an aqueous metal cleaning composition which can be used effectively in immersion and impingement type parts washers so as to efficiently remove grease, oil and other contaminants from metal parts and which are safe to use and not a hazard to the environment in use or upon disposal.
Still another object of the present invention is to provide an aqueous metal cleaning composition which contains an ethoxylated thiol surfactant and which is formulated so as to greatly reduce if not eliminate the unpleasant odor associated with the surfactant.
Yet another object of the present invention is to provide an aqueous cleaning composition containing an ethoxylated thiol surfactant and which does not have the unpleasant odor associated with the surfactant and, thus, can be effectively used in immersion and impingement type parts washers and in the relatively closed commercial settings in which such parts washers are utilized.